Sound recording



Sept. 24, 1940. HAMMER 2,215,925

SOUND RECORDINQ I Filed March 29, 19257 4 Sheets-Sheet l Sept. 24, B, D HAMMER scum) nmconnme Filed March 29, 193':

4 Sheets-Sheet 2 6 a v 0 L /I EU a w n M-// W W 6 W m Sept. 24, 1940.

4 Sheets-Sheet 3 W NRN Sept. 24, 1940. a HAMMER 2,215,925

' accident.

Patented Sept. 24,1940

UNITED, STATES PATENT-"OFFICE 2,215,925 7 SOUNDRECQRDING Bernard D. Hammer, Whittier, 0alif. Application March 29, 1937, Serial No; 133,584 4 Claims. "(or ire-4100.4) 1 T This invention relates to sound recording, and more particularly to the use of sound recording apparatus in conjunctionwith radio transmitting apparatus, whereby a permanent record is made of all sounds entering the microphone of the transmitting apparatus.

An object of the present invention is to provide 7 a sound recording apparatusco-operatively coupled with the radio transmitting set carriedby a conveyance such as a ship or an airplane, whereby messages can be transmitted from the conveyance while it is in operation and simultaneously a permanent record made of, such messages.

A more detailed object ofthis inventionis to adapt the. combination of recording apparatus and radio set of the general class described to use upon aircraft, and more particularly upon commercial freight and passenger carrying aircraft, in such a manner as to'make it possible to produce an adequate ships log required as a matter Ofordinary routine, but without the consumption of any material amount of time and without having to do any actual writing. Whereas such a permanent record is merely a matter of routine, it is required of all commercial airline operatives and it assumes great significance whenever an accidentoccurs, inasmuch as the actual flying conditions encountered by the aircraft just prior to the accident may have had a distinct bearingupon the cause'or causes of the However, the written log is often highly unsatisfactory, inasmuch as the writing thereof requires much time on the part of the ships officer to whom the duty is assigned, and

much of his attention which had better be directed toward the'safe manipulation of his craft and its passengers. Moreover, making a written log depends to large measure upon the exercise of memory by the oflicer, for the reason that it is physically impossible to make notations in writing of all the events, weather conditions, instru-- ment readings and other data as fast as they occur or as fast as they are observed. Those inherent disadvantages of a written log of an airplane are more pronounced in times of stress, such as the last few seconds just preceding a serious crash, becauseall of the efforts of the ofiicer are then needed more than everfor the skillful manipulation of his ship in the attempt to avoid the impending accident. Even if this were not so, the excitement of the moment under which the'pilot and his assistant are laboring is apt to be so great that writing a record of the actual cause of the impending crashes then observed is wholly out of the questionand of course it is these actual causes that hold the greatest interest for all parties concerned afterthe crash has occurred and an investigation is' being made to determine what those; causes Were inasmuch bles and airplanes are commonly provided. It.

actual cause of the accident,

.as itis: principally by a realization and analysis of the causes of aircraftaccidents that it ismade possible to make provision for the avoidance of future accidents.

Further than this,when an airliner does crash,- 5 it and its entire cargo are not infrequently consumed by fire; thus, destroying the ships logand making just that much more diflicult the determination of the cause ,or causes of ,the'accident. It is apparent,,.therefore, that the customary type of written'log of an aircraft (or any other ,type of conveyance. for that matter) frequently fails utterly under the very circumstance where it would be most helpful were its preparation not subject to the physical limitations referred to.

It is a further object of the present invention, therefore, to provide means whereby either the pilot or one of the other members of the crew can dictate any remarks which later might prove to be of significance-in other words, by speaking 20 into a microphone to make a permanent record ing apparatus whereby a-log may be made instantly as described with the radio transmitting set with which such conveyances as ships dirigishould be explained-that in air transport service ,one of the members of the ships crew is required to report to his ground station at regular intervals, giving the ships position and speed, weather conditions and other data whereby an accurate 40 check of the airplanes progress along its course ,can be maintained by the ground crew. These data are the principal items constituting the usual ships log which previously has had to be written out in longhand, thus requiring duplication which by this invention is made unnecessary, inasmuch by proper manipulation of a switch the remarks tobe transferred by radio to the ground station can be transmitted to and recorded by the recording apparatus. 7

A still further object is so to mount the recording apparatus that it is amply protected from the vibration and tilting out offtrue horizontal position to which the airplane is subject during flight and from the shock incident to actual crack-up of the airplane-so that any record which had been made upto the time of the crash will be' preserved to serve for. what value it may have toward permitting investigators to determine the A still further object is to insulate the recording apparatus in such manner that even though the entire ship and its cargo be destroyed by fire the record still will be preserved.

Yet another object is to combine with the apparatus hereinabove described a warning signal so arranged that the pilot or other duly appointed member of the ships crew is automatically warned at the prescribed intervals of time when he should report to his ground station, the mechanism being so arranged that the warning signa persists until the report actually is made.

The invention possesses other objects and features of advantage, some of which, with-the foregoing, will be set forth in the following description of the preferred form of my invention which is illustrated in the drawings accompanying andforming part of .the specification. It is to be understood that I do not limit myself to the showing made by the said drawings and description, as I may adopt variations of the preferred form within the scope of my invention as set forth in the claims.

Referring to the drawings:

Fig. l is a diagrammatic view showing the outline of the fuselage of an airplane and a schematic layout of the sound recording apparatus and associated devices embodying the principles of the present invention.

Fig.2 is an enlarged diagrammatic view showing a wiring diagram of the device of the present invention.

Fig. 3 is an enlarged top plan view of one embodiment of the sound recording apparatus which forms one of the units of the combination representing the subject matter of the present invention. I

, Fig. 4 is a view in end elevation, partly broken away and showing in vertical section the sound head of the sound recorder of Fig. 3.

v Fig. 5 is a View in front elevation, the direction of View being indicated by the arrows 5 of Figs. 3 and 4, this view being partly broken away and shown in section.

Fig. 6 isan enlarged view in transverse vertical section taken through the sound head and a portion of the record with which it is cooperatively associated;

' Fig. '7 is a transverse sectional view taken upon the line '|'l of Fig. 6 with the direction of view as indicated.

v Fig, 8 is a transverse sectional view taken upon the line 88 of Fig. 6 with the direction of View as indicated.

In terms of broad inclusion, the present invention contemplates the combination of a means of conveyance such as a ship or airplane, a radio transmitting set carried thereby and through the expedient of which messages may be transmitted while the conveyance is in operation, and a sound recording apparatus whereby a permanent record may be made of any or all messages transmitted by means of the radio set. Appropriate controls are provided whereby both the transmitting set and the recording apparatus may be made operable independently of each other or simultaneously as the operator may elect. Various other details of refinement will be explained in greater detail hereinbelow.

I, have shown on Figs. 1 and 2 in schematic form a proposed arrangement of parts within the fuselage ll of a conventional transport airplane which cooperate with each other to present the combination forming the subject matter of the present invention. Among these elements are a sound recording apparatus l2, a radio transmitting set, the amplifier of which is indicated at l3, a microphone I4 of suitable design, a conventional interval timer 16, an electrical relay l1 associated therewith, a warning signal I3, a control switch I9, and a dictating switch 20, all of which will be explained in greater detail hereinbelow.

Suffice it for the purpose of the present disclosure to explain that the radio set of which the amplifier I3 is indicated diagrammatically is not illustrated, inasmuch as any suitable and conventional transmitting set may be employed advantageously in connection with the present invention. Preferably it is a-short wave transmitter, inasmuch as this-is the type commonly employed for the type of service for which the present invention is primarily intended. In order for the pilotor other member of the crew of the airplane tocause a permanent record to be made of any comments, it is necessary only for him to lift the microphone Mfrom a receiver hook 2! or other element provided to hold the microphone when it is out of use, and to close a switch disposed inconvenient location, before talking into the microphone. The hook is movable, and when the weight of the microphone l l is removed therefrom, it operates to close switch contacts which control the motor circuit of the sound recorder.

The sound recording apparatus receives its actuating energy from the battery 28. It comprises the housing 36 within which is mounted a'motor 37, the speed of which can accurately be regulated by a suitable governor 38, of any suitable design and preferably provided with an adjustment mechanism 39, regulable as by a manually operable thumb screw 4|. A shaft 42 of the motor 37 carries a pulley 43, engaged by a belt 44, both runs of which extend upwards through suitable apertures in the top 46 of the housing 35 to engage also a larger, driven pulley 41, which is freely revoluble upon a tubular spindle 38 carried by a frame 49 mounted upon the top Q5 of the housing 36. The outer face of the hub of the driven pulley 41 carries a plurality of ratchet teeth 5| releasably engageable by complementary ratchet teeth 52 carried by a clutch plate 53 which is affixed to a shaft 5 l which extends through the tubular spindle 48 and is revoluble thereinside and which is axially movable far enough to permit engagement or disengagement of the teeth 52 of the clutch plate 53 with or from, respectively, the teeth iii of the pulley M. Beyond the spindle 48 from the clutch plate 53 the'shaft 54 carries a gear 56 which enmeshes another gear 51 which is affixedto the shaft 53 upon which a drum 59 is mounted, to be rotated thereby. This drum is of elongated cylindrical form and is adapted to receive a cylindrical record M of wax or other suitable material adapted to receive the impression of a vibrating needle so as to produce the sound track impression in the wax, which results from the transmission of electrical impulses to the sound head 51. It should be explained that these impulses are delivered to the sound head by a suitable circuit 59 leading from the amplifier I3, so that a record can be made of any speech or other sound entering the microphone l4 while the contacts 2 and 24 are engaged.

The end 62 of the drum 6| opposite that with which the gear 51 is associated is supported by a bracket 63 which is pivoted to the tail piece 64 of the frame '49 as by'a pin 66 so as to permit a stub shaft 61 whichiscarried by, the arm 63 optionally to beinto supporting contact with a coni: calpoint-jB on the, shaft 158 or away'from, the point 68, so astopermit removal of a record 6| from-the drum-62 or they replacement thereof by anotherrrecord.

;, ,The shaft 54.;and plate .53. of the clutch are caused to move axially through the expedient; of the clutchoperating, mechanism 1 I comprising an electro-magnet I2 adjacent the core I3 on which the armature is so disposed that it is adapted to be-drawn vertically downward when the elece trQ-magnet I2 is; energized. The armature I4 is connected bya lock-18 with a-rocker arm 11 mounted upon a bracket, I8. A spring "I9 0011-, tinually urges the rocker arm ,"Il to move in that direction which lifts the armature I4 away from the core I3 of the electro-magnet 'I2 and which causes, the plate52 of the, clutch to move to its disengaginggposition, which movement is effected through the expedient of a finger 8| carried by the rocker arm'I'I andhaving aroller 82 thereon operativel y. disposed within the annular groove I 83 in theclutch plate 53.

, Thus; it may be seen that-when the motor 3I -is energized the, shaft 42 anddriven pulley 411 will becaused to revolve at constant speed, as determined by the adjustment of the thumb screw 4|.

- Thenby energization of the electromagnet I2 the clutchplate 52 is broughtinto engagement with the teeth 5| of ;the pulley 41, causing the shaft 54 to rotate, which impartsrotation to the drum 62 carrying the record 6| A sound head indicated in its entirety at 9|,.is

disposed closely adjacentthe face of the record Gland is mounted formovement longitudinally with respect thereto through the expedientof upperand lower .ways 92 and 93 respectively; The

lower way 93 is preferably in the form of a rod of circular cross-sectional, configuration. It carries an arm 94 which is movable axiallyinsliding movement upon the -rod 93, inasmuch as the rod 93 extends througha cylindrical ,hub 96 formed on the lower end of the arm 94. Advance of the arm 94 along the rod 93 is effected through the expedient of a finger 9.1, the, outer end of which carries a few segmental threads which engage the threads 98 of a feed rod; 99 revolubly'carriedby the frame 49, a gear .;IOI afiixed to the feed rod 99 is enmeshed with-the'gear 5'I-whereby the drum I52 isrotated. Hence when the threads of the finger 9'I are engaged with the threads-98 of the-feed rod 99 and the drum 62 caused to rotate, the arm andsound head; 9| carried thereby will be caused to move longitudinally withrespectto the drum 62 and at a" speed bearing a predetermined relationship to the speed of rotation of the d -.q. a.

The upper end of the-arm 94carries small rollers I02, which are disposed in rolling engagement with the'under side of, the upper way 92.; The parts areso positionedpand arranged that upward movement of thearm 94 and-roller I02 ca-r-' ried therebyis necessary tov efiect disengagement of a feed finger 91 from the-feedrod 99, and of course this is prevented without movement of ,the upper guide way; 92, inasmuchv as, the .roller. I02 engages the under side thereof. ,;Consequently the upper gear rod92 is:pivotedat one end'as by. a

pin I03, whereas theiother end is engaged within a notch I04 in .the inner faceof an extension I06 of the bracket-633 Hence when the bracket 1 Adjacentjthe upper end of the arm 94 and preferably integrally formed thereon is a housing I II within which the sound head 9| is installed. This sound head 9| comprises a suitable cage II2 which is pivotedto the housing III adjacento-ne end thereof as by a pin I I3. The other end of the cage I I2 is permitted a limited degree of vertical movement within the housing III, the extent of and armature I23is carried by the cage H2. The

armature; I23 is pivoted as at I24 and the end I26 of the armature I23 remote from the solenoid I2I carries a vibratory needle I2'I which extends into record making engagement with the record cylinunder compression between the armature I23 and 1 the cage vI I2 continually urges the needle I2'I toward the record. Movement of the cage II2 t0- ward the record is limited by means of a roller I29 journaled upon the outer end of the cage and disposed? in rolling engagement with the. outer comder- 6| carried by thedrumBZ. A coil spring I28 face of the record 6|. Thus it may be seen that because of the relative movement which I have madepossible'between the cage I I 2 and the housingII I, the :needle I2'I will always be maintained in proper relationship with respect to the record even though thehousing III is subjected to a considerable degree of vibration or actual movemer t toward or away from the .record. 'A relativelv soft spring I3I, preferably of the'lift variety, is interposed between the cage I I2 and the housing :I II,' to insurethat the needle I21 will be maintained in proper position with respect to the record, even though theentire apparatus'be in verted. -1

'Althoughany suitablesource of electrical ener- I gy may be employed for the energization of the motor 31 and the clutch operating'mechanism' II of the sound reproducing apparatus, they preferably-derive their energization from the same source 28 as that which energizes the radio transmitting set. ,I-Ience, in the embodiment herein being described, the motor 31 has associated therewith a'circuit comprising a conductor 'I5I motor 31, another conductor I52 leading toa contact element I53 within the control switch I9, and still. another conductor I54 leading from the-associatedswitchcontact I56 back to the other terminalgof the 'battery128. The contacts I53 and I5 Ii,are5so arranged with respect to each other and with 'respect'to thereceiver hook 2I that when the: microphone is lifted from the hook i the 'expedient'ofa conductor I57 leading from the conductor I5I and hence already in electrical. communication with one terminal of the battery 28. Another conductor I58 leads fromthe electromagnet I2 to a switch contact I59, which is disposed. within the dictating switch 20; The switchcontacts 23 and24 previously described as leading from one terminal of the battery 28 to the being arranged to control the microphone circuit 2,6 are adaptedtov be brought into electrical communication; with: each other when preferably manual pressure is exerted on a switch 29, which is disposed in position conveniently accessible to the operator. Preferably this switch is'mounted upon the control wheel or upon the joy stick, and in the event that multiple'controls are pro- Vided, one such switch 28 is mounted upon each of such members.

Still another set of contacts I6I and I62 are disposed inside the control switch I9, these contacts, however, being in electrical communication with each other when the receiver hook is down and the other switch contacts separated from each other. The contact I6I is connected as by a conductor E 63 to one terminal-of the battery 28, whereas the contact i522 is connected by a conductor I64 which leads to one terminal of the light l8. The other terminal of the light I8 is connected by a conductor I66 to one terminal of the automatic timing device 66, and the other terminal of the timer i6 is connected as by a conductor E61 to the other terminal of the battery 28,

with the result that the signal light I8 is energized whenever the receiver hook 2i is depressed and the constantly moving contact I68 of the timer I6 is in contact with any one of the several stationary contacts i653 of the timer I6.

The relay I1 is associated with the timer I6 and the light I8 so as to cause the light I8 to remain energized until the pilot or one of his 30:

assistants lifts the receiver hook 2I, as'by removing the microphone. I6 therefrom, which he must do in order to make a report either to his log or to his ground station by means of the short wave radio set. The conductor. I64 from the switch contact.I6I also leads to one terminal of the electromagnet I'II of the relay I1. From the conductor I61 which leads to the stationary contacts I69 of the timer I6, a secondary conductor I12 is shunted around the timer I6 and leads to the armature I13, which is adapted to bemoved to the left, as viewedupon Fig. 2, when the electromagnet III is energized. Such movement of the armature I13 brings its contact I14 into engagement with a contact I16 which is in electrical communication with the conductor I66 leading to the opposite terminal of the signal light I8 from that which is connected to the con- 'ductor I64.

A function of the relay I1 is to insure that the light I8 remains illuminated even after the moving contact I68 of the timer I6 has become dis engaged from the stationary contact I69, which had last been engaged thereby, until such time as the pilot or his assistant actually lifts the microphone I 8, as is required for him to make his periodic report. It will be observed that the microphone hook 2| carries an extension I8I which engages the. contact I62 when the hook 2! is down, bringing the contact I62 into engagement with the contact I6I. However, when the hook 25 is lifted, the contacts I6I and I62 are separated, suitable resilient means (not shown) being providedto normally hold these contacts separate, as is also shownin the case of the contacts I53 and 56, and 24;

Operation Since the timer I6 operates by clockwork (not shown) or other means for bringing the movable contact I68 thereof into engagement with one of its stationary contacts I68 at regular'intervals of time, say every fifteen minutes, the warning light I8, which preferably is positioned upon :the instrument boardiso as to command- I56 and I59, and23.

the attention of the operator of the airplane or other member of the crew, will be illuminated at regular intervals, these intervals corresponding to the periods of time at the end of which the ground station requires a report from the airplane. Normally, of course, the microphone I4 rests upon the hook 2I so that the finger I8I of the hook holds the contacts I6I and I62 inelectrical communication with each other. Accordingly, when the movable contact I68 of the timer I6 next engages any one of the stationary contacts I69, current will flow from the battery through the conductor I61, the timer I6, and the conductor I66 to the light I8, thence by way of the conductor I64 to the stationary contacts I62 and I6I, and thence back to the battery 28 by the conductor I63. In the event that the operator delays making his report until such time as the movable contact I68 has passed out of engagement with the fixed contact I69, the light I8 will remain illuminated, owing to the fact that when the light I8 is further energized as described, current also flows through the electromagnet I1I which is connected in parallel with the light I8. This energization of the electromagnet lllcauses the contact I14 to engage the contact I16, so that after the flow of current through the timer is interrupted it will continue to flow to the light I8 by way of the shunt only de-energizing the light I8 but also the elec- 1 tromagnet I1I, permitting the contacts I14 and I16:to separate, with the result that even though the microphone again be placed upon the hook 2I shortly thereafter, the light I8 will not again be energized until the movable contact I68 of the timer I 6 engages the next successive fixed contact I69.

When the hook 2I rises (it being understood that such movement is insured as soon as the microphone I4 is lifted therefrom), through the expedient of suitable resilient or other urging means (not shown), the finger I15 on the hook 2I'v moves the contact I53 into engagement with the contact I56. This completes the circuit which includes both the battery 28 and the motor 31 of the sound recording apparatus. Energization of the motor 31 before any of the other circuits are completed is desirable, inasmuch as it takes an appreciable period for the motor 31 to gain its true speed, and by combining this circuitof' the motor slightly before completion of thecircuit of the .clutch actuating mechanism, it is assured that the motor will be running at full speed before the clutch 53 is engaged to cause the record 6| to revolve.

' In the event that the operator desires to make a record of any comments without sending such comment over his'short wave transmitting apparatus, he operates the dictating switch 28 to bring the contact I60, which is connected to the battery 28, into engagement with the contact I59, .thus effecting energization of the clutchengaging mechanism H, and causing the cylinder of the recording apparatus to revolve. The switch 28 is so arranged that when the contacts I59 and I68 are electrically engaged, the contacts 23 and 24 of the microphone circuit also are engaged; and, as the motor 31 is already in'operation as the result of thefact that the microphone-has previously been liftedfrom its phone will be recorded upon the record 6|. As explained, the amplifier portion I3 of the short wave transmitting set remains energized while the airplane is in operation, so that no time is required for the tubes thereof to become heated; hence the apparatus is in .condition for recordation almost instantly, so that there need be no loss of time for the operator tomake a permanent record of any comments such as statement of the condition of the weather, instrument readings, the ships position, or the like; or in times of excitement, such as might be expected in the short intervals just before an impending accident, the operator is given opportunity to cause to be preserved his observations as to the cause of that accident. Previously it has largely been a matter of pure conjecture as to the .cause of manyof the recent airplane accidents, and the lack of positive information has been a serious handicap to the adoption of regulations and new design which probably would aid materially in the avoidance of future similar accidents. Such action on the part of the operator requires no more time other than merely that required for the recitation of the words necessary to describe the actual condition and requires practically no distraction of the operators mental or physical efiorts toward avoidance of the accident.

By mounting the sound recording apparatus l2 in a fireand heat-proof compartment 201, having a lid 202 of similar construction, and by mounting this compartment in the extreme after end of the empannage, this part of the airplane being that which is least liable to destruction in the event of a serious crash, it is believed that in most instances at least the record on the sound recording apparatus I2 will be preserved, even tho-ugh the rest of the ship be substantially completely demolished. In order to protect the apparatus from the shock which is incident tosuch a crash, as wellas from the vibration to which the entire conveyance is subjected, due to the operation of its driving engines, a compartment is supported on the tail of the ship, upon a plurality of springs 203, of such a nature that they provide ample means of absorbing these shocks and vibration.

It is within the scope of the present invention to arrange the switch controls in such a manner that the transmitting set can be energized without completing the circuit whereby sound is transmitted in the form of electrical impulses to the recording head of the sound recording apparatus. opening a secondary switch 2 in the circuit 65.! interconnecting the radio l3 and the sound head 9|. In order that there shall be no wastage of space on the record 6|, it is preferred that another switch 2l2 be provided in the circuit controlling energization of the clutch mechanism. If desired, these switches can all *be mounted in a single housing and operated by a single control, so that by moving an indicator thereon to selected position, the operator can'instantly set the appa ratus to operate as desired.

I claim:

1. In a sound recording apparatus of the character described, means for supporting a record and moving it at constant speed, a guiding way thereadjacent, an arm movably mounted on said way, a housing on said arm, means for advancing said arm along said way withsaid housing mov-- ing across the face of said record in close proximity thereto, a sound head mounted for move- This can conveniently be accomplished by ment within said housing toward and away from said record and comprising a vibratory needle extending into contact With said record, a means for vibrating said needle, spring means interposed between said housing and head and urging said sound head toward said record, and a roller carried by said sound head and engaging said record to hold said head at predetermined spac-. ing from said record, regardless of the position of saidrecording apparatus with respect to the horizontal. p

2. In a sound recording apparatus of the character described, means for supporting a record and moving it at a constant speed, a guiding way thereadjacent, an arm movably mounted on said way, a housing on said arm, means for advancing said arm along said way with saidhousing moving across the face of said record in close proximity thereto, a sound head mounted for movement within said housing toward and away from said record and comprising a vibratory needle, extending into contact with a record carried by said supporting means, a means for vibrating said needle, spring means interposed between said housing and head and urging said sound head toward said record, a roller carried by said sound head and engaging said record to hold said head at predetermined spacing from said record in all positions of said apparatus with respect to the horizontal, a means for mounting said sound recording apparatus upon a vehicle comprising a casing of heat-resistant and substantially shock-proof material enclosing said apparatus, and a plurality of springs between which said casing is suspended to cushion said apparatus from vibration incident to operation of said apparatus and from shock incident to disabling of said apparatus.

3. In a sound recordingapparatus, means supporting a record and moving it at constant speed, an arm movably mounted thereadjacent, means for advancing said arm at a predetermined rate with respect to the speed of said record, and a sound ,head carried by said arm and comprising a cage, a solenoid carried by said cage, and armature pivoted on said cage and disposed in operative relation to said solenoid, a needle carried by said armature and extending into contact with said record, a spring associated with said armature and pressing said needle into contact with said record, and means carried by said armature and engaging said record to limit the distance the armature can be moved toward said record by said associated spring.

4. In a sound recording apparatus, means supporting a record and moving it at constant speed, an arm movably mounted thereadjacent, means for advancing said arm at a predetermined rate with respect to the speed of said record, and a sound head carried by said arm and comprising a cage movable with respect to said arm, spring means urging said cage toward said record, a solenoid carried by said cage, and an armature pivoted on said cage and disposed in operative relation to said solenoid, a needle carried by said armature and extending into contact with said record, a spring associated with said armature and pressing said needle into contact with said record, and means carried by said armature and engaging said record tolimit the distance the armature can be moved toward said record by said associated spring.

BERNARD D. HAMMER. 

